Deposition of ScAlN Thin Film Using RF-Sputtering Method

High-Sc-content ScAlN thin films have attracted significant attention because of their strong piezoelectric properties. Akiyama et al. found that the piezoelectricity of ScAlN thin films increased monotonically with increasing Sc concentration, r. The piezoelectricity reached a maximum at r = 43 at%, at which the piezoelectric coefficient, d(33), was five times that of pure AlN. The Akiyama group showed that the d33 of a ScAlN thin film with a high Sc content and wurtzite structure would be much larger than that of the 43 at% Sc film, as calculated by first-principles methods. However, ScAlN thin films typically exhibit a rock-salt rather than a wurtzite structure with increasing Sc content, because ScN has a rock-salt structure at thermal equilibrium. In this report, we studied the deposition of ScAlN thin films using a RF sputtering method, and it's characterization to clarify the deposition conditions needed for films with high piezoelectricity. The result of micro-Raman spectroscopy measurement shows that, as the Sc content of the ScAlN thin film increases, the peak at similar to 800 nm(-1) of the A1 mode, due to Sc atoms in the Al sites of the wurtzite structure, shifts to lower frequency for these sputtering conditions. This means that Sc atoms occupy Al sites in the wurtzite structure in the thin film until the Sc content reaches 33%. This phenomenon was also observed for AlGaN thin films. The peak near 700 cm(-1) for the ScN thin film, ascribed to a cubic structure, is deformed with increasing Al content.